1. Field of the Invention
This invention relates to a valve apparatus and method for pressurizing fluids, such as gas or liquid, which can then be quickly released or dumped when over-pressurized, to transform continuous fluid flow into pulsed waterjets without significant energy losses. This invention is particularly suitable for use with liquids, such as water, that operate at relatively high pressures and generate high-speed pulsed fluid jets which have high impact energy levels and which travel great distances.
2. Description of Prior Art
The utility of high-speed fluid jets, such as waterjets, is well known. Continuous waterjets having various flow rates and velocities are used in a wide range of applications. One basic process for generating a continuous waterjet is relatively simple, wherein water is transported to a suitable pump to raise the operating pressure, the pressurized water is then communicated through tubes or hoses to a suitable nozzle, and the pressurized water is ejected through the nozzle to form a coherent waterjet. The particular type of conventional system can vary depending upon the different complexities associated with an intended application. The discharge velocity and the energy content of the waterjet can vary among different conventional systems, and are often a function of the pressure and the power input of the system.
Conventional waterjets are used in different civil, commercial and industrial applications. One common use is for firefighting processes, in which relatively large diesel engine-driven crankshaft pumps are used to pressurize water at moderately high pressures, such as at several hundred pounds per square inch (psi), and at relatively high flow rates. In firefighting operations, it is important for a nozzle, such as a long and smooth nozzle, to generate a coherent waterjet capable of traveling a significantly long distance. High-speed waterjets are also created by relatively compact hand-held jetting lances, for cleaning and blasting industrial structures and equipment at water pressures up to about 35,000 psi. Water can be pressurized to pressures up to about 60,000 psi, and discharged at supersonic velocities, with pressure intensifiers. Such waterjets are used in factories, normally with automated robots, to cut a wide variety of materials such as paper products, leathers, fabrics, food items and many other industrial products.
Conventional systems also mix selected particulate materials, such as industrial abrasives, to a high-speed waterjet to generate what is known as an abrasive waterjet (AWJ) for cutting relatively hard material such as glass, plastics, laminates, composite, alloys, metals, rock and concrete. Experiments are now being conducted with water-based abrasive slurries, for generating abrasive waterjets; such processes involve direct or indirect pressurization of abrasive slurries and discharging pressurized slurries through a nozzle, to form a high-speed slurry jet. The relatively high velocities achieved by the abrasive particles offer a slurry jet with unmatched cutting capabilities.
Waterjet systems can be characterized by two basic system parameters: system pressure and energy output. In firefighting applications, a waterjet system pressure is relatively low but the mass flow rate is relatively high, and thus the emphasis of the system is directed toward delivery distance of the waterjet. In waterjet material-cutting applications, the system has quite opposite requirements wherein the mass flow rate is relatively low but the system pressure is relatively high. In both applications, the waterjet energy is basically defined as a product of mass flow rate and system pressure. The system equipment delivers energy at a relatively steady rate, which is a common characteristic of continuous waterjet systems. Such continuous waterjet systems can be modeled as electrical systems wherein electrons are equivalent to water, voltage is equivalent to water pressure, current is equivalent to flow rate, electrical conductors are equivalent to hoses or conduits, electrodes are equivalent to water nozzles, and an electrical discharge at an electrode is equivalent to a waterjet.
Relatively powerful electrical discharge can be produced by raising a voltage across two electrodes, particularly if relatively large capacitors are used to store a large amount of energy and then quickly discharge the energy. A similar situation exists in waterjet systems. In many waterjet applications, it is very desirable and advantageous if the waterjet energy can be stored and ejected through a nozzle in a pulsed jet rather than a continuous jet. It is quite desirable in many applications to deliver a relatively large amount of waterjet energy to a target material, in a concentrated fashion and within a relatively short time duration. This is the realm of pulsed waterjet (PWJ) technology.
The benefits of relatively high-speed PWJ have been recognized and appreciated in mining applications, due to the particular nature of rock and minerals. Such porous materials are known to have relatively high compressive strength but relatively low tensile strength, so that the water can produce fractures in such materials. Continuous waterjets applied in a conventional fashion, even at relatively high pressures, result in localized failure, such as formation of slots and kerfs. On the other hand, pulsed waterjets can caused rocks and minerals to fail in a more pronounced manner as compared to that possible with continuous waterjets operating at a same energy level. If a sufficiently large slug of relatively high-speed waterjet is delivered to rock material in a relatively short time, the rock material can fail catastrophically, in a manner similar to explosive forces. Even in ordinary waterjet cleaning and blasting operations, discrete waterjets are preferred over continuous waterjets, for efficiently and effectively removing contaminants.
Other lesser known applications exist where suitable pulsed waterjets could significantly impact the operation, for example, pulsed waterjets may be quite suitable for injecting materials into the ground for applications such as in situ bioremediation. However, pulsed waterjet processes are often quite involved and many have been only laboratory curiosities, never reduced to practice.
Pulsed waterjet processes can be characterized by other system parameters, such as pulsation factors which define the pulse length, spacing and other features. Such pulsation factors may be relatively important in many applications and are governed by the particular system application and type of pulsed waterjet generated.
Many different methods can be used to generate pulsed fluid jets. A relatively simple method is to use a pump with an unbalanced pressure discharge, such that a jet discharged from a nozzle has a naturally fluctuating velocity, if the distance between the pump and the nozzle is not too great. Another conventional method employs a nozzle that segments a continuous stream fluid jet into discrete slugs. Impact extrusion, pressure extrusion and cumulation methods for waterjetting have been conventionally used to generate relatively high-power pulsed waterjets, for applications such as fracturing rock and concrete.
U.S. Pat. No. 4,074,858 teaches a pressure extrusion process for generating relatively high-power and relatively high-pressure pulsed waterjets capable of fracturing concrete pavement. Compressed gas, such as nitrogen, is used to store energy. Two sets of pistons are used to cock and drive a plunger for transferring the stored energy to the fluid, such as water. Hydraulic fluid is often the working fluid for the required power input. A fast-acting valve is used to fire an oil port in a controlled fashion and thus the water is discharged from a nozzle by a fast-traveling plunger within a high-pressure cylinder. U.S. Pat. No. 4,074,858 discloses a plunger that must first pressurize water prior to forming a waterjet at a nozzle, even though the pressure within a cylinder may not be steady during plunger travel and may not even be critical to the end result. Such process works relatively well but is rather limited in usefulness. One limitation relates to the speed of the plunger which inherently depends upon working fluid flow, which is situated between the compressed gas and a power piston. Oil is inherently slower than gas in similar flow conditions and oil velocity is affected by different viscosities. Another limitation relates to an absence of a water valve at an outlet, to prevent leakage through the nozzle while charging. Water leakage can be quite substantial in vertical, downward applications of pulsed waterjet processes, and partial filling of the chamber can result in undesirable shocks and performance losses.
U.S. Pat. No. 4,190,202 teaches a process for generating high-power and high-pressure pulsed waterjets, wherein a restrictive oil port is eliminated and a cocking piston is moved into a same chamber with a power piston, to increase the piston and plunger speed, and to improve firing control, a relatively difficult task in high-power pulsed-jet processes. Such process also allows the cocking gas to be evacuated prior to firing, thus improving energy transfer from gas to water. However, there is still a need for a suitable water valve that prevents nozzle leakage prior to firing, and there is still the need for eliminating premature firing.
U.S. Pat. No. 4,607,792 teaches a pulsed waterjet produced by impacting water with a reciprocating piston within a reciprocating cylinder equipped with a cumulation nozzle. Pressurized gas supplies necessary energy to power the piston and inertia of the piston along with reciprocating motion of the nozzle cylinder produces oscillating action. It is possible to produce rates of up to several pulses per second with such process. U.S. Pat. No. 4,607,792 is a good example of one of many processes for generating pulsed waterjets that have relatively low mass per pulse but relatively high repetitive rates. Such process can produce pulse jets at relatively high velocities, if the power input is high and the cumulation nozzle is adequately constructed in terms of internal profile and smoothness, which are two relatively difficult manufacturing tasks. In order to accelerate a piston of significant mass to a relatively high velocity within a relatively short time and distance, explosives or detonation of a fuel-air mixture is used, neither of which is desirable in many applications. If compressed gas is used, only compressed air is practical and only when delivered at relatively low pressures, due to cost considerations. As a result, the pulsed waterjet generated with air compressors has relatively low velocity and cannot generate impact forces necessary to fracture rock and concrete, for example. Furthermore, the absence of a restricting valve to minimize leakage at the nozzle can be a disadvantage with the invention taught by U.S. Pat. No. 4,607,792.
U.S. Pat. No. 4,573,637 teaches a pulsed-jet process which uses energy stored in a high-pressure fluid to generate a high-speed jet through a cumulation nozzle and an oscillating self-actuating valve. Liquid such as water is relatively incompressible, even at high-pressures, and the amount of energy available which can be released to generate and sustain high-speed jet pulses is limited. Even when using a cumulation nozzle, energy contained in each pulsed waterjet is not high enough to adequately fracture or damage material such as rock and concrete.
Other conventional pulsed waterjet devices and processes are available, which use cumulation nozzles that have hyperbolic or other internal fluid passages for accelerating fluid flow velocities. The valves for such nozzles are relatively difficult and expensive to manufacture and there is no particular design to which manufacturers conform. Many conventional cumulation nozzles used in pulsed waterjet processes lack scientific evidence to substantiate their virtues, thus, a survey of conventional devices and processes show that many high-powered pulsed waterjet processes only exist as laboratory projects. Many unresolved difficulties are associated with the equipment design. Practical devices are not commercially available for particular jobs, such as fracturing rock and concrete. There is an apparent need for an apparatus and method for producing a high-powered pulsed waterjet with a relatively inexpensive and practical device that is easy to manufacture.